The invention concerns a valve train of an internal combustion engine, said valve train comprising one or more switchable support elements that are arranged with an inner element for relative axial displacement in a reception of a cylinder head of the internal combustion engine, which inner element extends beyond the reception by a head comprising a support for a finger lever, a coupling means for a selective coupling of the inner element relative to the reception in an axially extended state of the inner element out of the reception being associated to the support element, while the inner element is biased away from the reception by at least one spring.
A generic valve train of the pre-cited type is disclosed in DE 44 22 340 A1. This valve train has the inherent drawback that its support element has a relatively large overall height. As a person skilled in the art will see from the figure, due to the compression spring being arranged under the inner element, a considerably large design space is required. If such a support element is to be integrated, for example, into existing engine designs, its relatively large height can lead to design space problems. Also, it is often not possible to deepen the reception bore for the support element in the cylinder head because one would penetrate into the region of inlet, outlet and cooling channels or the like.
Other known switchable support elements have a relatively large overall width due to their special concentric spring arrangement, or due to other design features.
It is an object of the invention to provide a valve train of the pre-cited type in which the aforesaid drawbacks are eliminated.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the spring is arranged axially offset next to the support element and is coupled to the inner element by a crossbar.
Alternatively, the invention achieves the above objects in an embodiment comprising two support elements by the fact that the two support elements are loaded by a common spring that extends at least substantially outside of the support elements.
The design space problems discussed above are eliminated in a simple manner by the measures proposed by the invention.
Thus, the invention proposes a valve train comprising at least one or, alternatively, two support elements, that require only a small design space and can therefore be integrated in most cases into existing engine designs. As a result, engine manufacturers do not need to make complicated modifications to the overall design of the engines. Distances once defined, for instance the distance of the camshaft axis from the crankshaft axis, can be retained.
In particular, due to the external and laterally offset arrangement of the spring, the proposed valve train including the support elements is relatively flat compared to prior art configurations, for example, compared also to that disclosed in DE 197 105 78 A1.
It is conceivable to use a variety of spring elements such as flat coil springs and torque rods, but also pneumatic or magnetic and other similar means. Due to the design space freedom obtained by the external positioning of the springs, it is possible to realize higher spring forces. In the uncoupled state of the support element, this also enables a reliable lost motion stroke of the inner element at high to very high engine speeds.
Although it is conceivable to use only one guide column and a single spring acting through a leg on the inner element, it is better to use at least two diametrically opposed guide columns with corresponding springs and have the inner element extend between these. By this measure, tilting and other similar accompanying negative effects are excluded.
Advantageously, according to a further feature of the invention, the springs surround the guide columns. However, it is also conceivable to use inter-inserted arrangements of the springs which, as proposed by way of example, can be configured as coil or flat coil springs.
The invention further proposes a simple means for connecting the crossbar to the inner element, viz., the crossbar surrounds the inner element quasi in the manner of spectacles. Alternatively, it is proposed to divide the crossbar and realize an engagement on the inner element through the two opposing legs of the crossbar thus obtained. Simple driving elements can be provided on the inner element, for example, in the form of circlips, annular extensions and the like.
If, for example, there are design space problems, but also to minimize costs, at least two support elements can be loaded by a single crossbar. A loading of the crossbar through the springs is preferably effected on the ends of the crossbar. If need be, even a central region of the crossbar situated between two support elements can be additionally loaded by a spring, and an additional guide column can also be provided for this spring.
As briefly mentioned above, in an alternative solution offered by the invention, two support elements can also be loaded by a common spring that can have a crossbar-type of geometry. According to an advantageous feature of the invention, the spring is made as a leaf spring or a stack of leaf springs. This measure is relatively inexpensive to realize and the mounting proves to be relatively simple. The upper front ends of the leaf spring can act on the inner elements of the two support elements in a direction to push them outwards.
It is proposed at the same time to hold a central region of the layers of the spring together by a connecting element such as a rivet. If need be, this rivet can sit on the cylinder head. This results in the creation of a quasi divided leaf spring stack.
Lower front ends of the leaf spring can be optionally supported on an edge of a housing for the inner element, or on a support on the cylinder head.
Although it is conceivable to let the inner element slide directly in the reception of the cylinder head, the invention advantageously proposes a housing that is fixed directly in the reception of the cylinder head.
For an indirect coupling of the inner element to the cylinder head, the invention proposes mechanical means, not further specified, such as pistons, balls, pins etc. These can be loaded in at least one direction of displacement by a hydraulic medium.
Finally, it is proposed to provide valve lash adjusting measures on the support element in the valve train. For example, each support element can comprise a hydraulic lash adjuster, known per se. This renders complicated mechanical adjusting measures adapted to defined operation cycles of the internal combustion engine superfluous.
The invention will now described with reference to the appended drawings.